How to Extend Your Vegetable Growing Season in Michigan

Introduction to Cold weather gardening

As a gardener in Detroit, Zone 6,  I see it repeated almost daily “don’t start your vegetable gardens until Memorial Day”. This advice that gardening only happens between the months of May and September has become so ingrained in everyone, and it is often perpetuated by local nurseries that only sell transplants and seeds at the beginning of our warm season. Tomatoes, eggplants, peppers, cucumbers, and squashes are not frost tolerant and are generally what most people think of when we think of vegetable gardens. The advice to not start your garden until the frost has passed is accurate… IF we are talking about warm season plants. 

However, here in the Midwest gardeners have the opportunity to extend their growing season in the spring and the fall. Cool season gardening occurs when soil is workable and not frozen, but there is still a chance of frost. When looking at your average high temperature for the month, your cool season months will have highs will be between 35-65 degrees Fahrenheit.  Here in Michigan, our cool seasons are March-April and October - November. 

As our cool seasons here are often two month “shoulder seasons”, it works out perfectly that many cool season vegetables have short days to maturity, meaning you can often have several harvests of cool season vegetables in your garden by the time you would want or need the vegetable bed real estate for tomatoes , or in the fall by the time it is too cold to grow without frost protection. 

The best cold-weather plants for the garden

Pea Seeds

Directly planted in my Detroit garden on St. Patrick’s Day!

Staples that you can often find in my cold weather garden include large and long plants such as kale, broccoli, leeks, cabbage, cauliflower, and brussels sprouts.  These are grown indoors that I will transplant into my garden. It is worth noting that learning how to grow these plants from seeds was important for the success of my cool season garden. Nurseries in my area simply do not carry these in the spring or fall. If seed starting is restrictive for you, there are plenty of suggestions of what to grow directly from seeds below. 

Cool season gardens also thrive with quick growing plants that often do great directly from seed and include carrots, peas, onions, lettuces, spinach, radishes, and beets. 

Does your garden have a trellis structure that you use in the summer for tomatoes or cucumbers? Peas will happily use that trellis in the cool weather months. 

These vegetables not only prefer to grow in cooler weather but also taste better when grown this way too! 

It is also worth noting that the fall is when garlic is traditionally planted. You can plant garlic cloves anytime before the ground really freezes up. This garlic will then stay in your beds through the winter, and resume growing in the spring. 

Tips to grow a cold-climate vegetable garden

A Low Tunnel

An easy addition to raised beds

• Should I cover my garden in the winter?

It’s complicated! When we are planting in the cool seasons, we are often bending the seasons just slightly. 

Plants like peas and onions can be started as soon as the ground is workable and don’t need to be covered if a frost unexpectedly happens at night. However, I would keep a fleece blanket, tarp, plastic cover, or something similar on hand for any other seedlings during nights of frost if you don’t have tunnels set up. While these cool season plants will grow, it is good to keep in mind that we might need to give them some help. 

Using season extension frost covers is an excellent way to continue growing your established fall garden well into the coldest months of winter. While most cool season vegetables are frost tolerant, they are usually only hard down to about 20 degrees. In my case, I can keep my garden uncovered and growing until about November. Once the nighttime lows begin to reach 20 I would cover my garden if I wanted to keep it going. 

In the spring, covering your garden beds can help warm the soil up a bit faster. After nighttime lows have passed 20 it is acceptable to transplant your larger plants into your garden, but low tunnels can still have a place in helping to protect your young plants from the bright sun, wind, and occasional cold night. 

• Should I start seeds indoors? 

Some cool weather plants will need to be started indoors, but not all have to be. 

Ideal choices for vegetables to start from seed directly in your garden outdoors  include carrots, peas, radishes, spinach, onions, and lettuces. Most of these cool weather loving vegetables will germinate when the soil starts heating up to about 45-50 degrees, although germination does take longer at this temperature than it would with soil that is closer to 70 degrees.  

Once your soil is workable it is time to start planting! 

Larger transplants that take a long time can be started indoors during the earlier winter months. I recommend starting broccoli, kale, cabbages, celery, and leeks indoors and then transplanting them outside a few weeks after you directly sow your seeds

Fall cool season gardens can be planted similarly to your spring garden. Direct sow at the end of summer quick growing plants such as carrots and greens. Larger cool weather crops such as kale and broccoli would need to be started indoors during the middle of summer and then transplanted outdoors at the end of the summer. 

• Should I grow in raised beds?

Growing in raised beds makes cold-climate vegetable gardening easier.  As a gardener, you will have more control over the temperature of your garden as you push your growing seasons. Raised beds will warm up in the spring faster than the ground does which will give your spring growing season a head start by a few weeks compared to in-ground garden temperatures. 

Raised beds are also incredibly easy to adapt with season extension accessories. Cold frames and frost clothes can be added to the beds and secured which will keep your garden going through the dead of winter. 

• How do I plant in the summer around my cool season vegetables?

When planning out your garden space throughout the growing year from spring to summer and back to cool season again in the fall it is important to note which plants will be staying and which plants will be giving up their space. 

Most cool season vegetables are ready to harvest quickly within two months and don’t need to be considered when planning your summer garden. These include salad greens, cilantro, kohlrabi, mustard, and radishes. 

Then there are some cool season vegetables that won’t be ready to harvest until a little after the summer season starts - cabbages, beets, broccoli, cool season herbs, and carrots. You will eventually be able to use this space in your garden, just not right after your frost date passes. 

Lastly, there are some plants that will need to continue to occupy space even through the summer - kale, leeks, celery, brussel sprouts, onions, potatoes are a few that come to mind. 

• How do I grow the most  cold-season vegetables in a small garden space?

It is important to pay attention to the days to maturity and how much space each vegetable takes up when planting. 

In a small garden space, it might be more useful to plant smaller plants such as spinach, lettuce, and carrots that you can harvest several times before summer rather than just a few large plants that would also occupy the space for a longer period of time. 

In small garden spaces, each square foot counts, and you can choose to spend 2 square feet growing 2 cabbages that need several months to reach maturity… OR you can choose to plant 18 spinach plants that you will have harvested a few times.